During magnetic resonance imaging the magnetic field may vary during the acquisition of the magnetic resonance image. For instance the switching of the magnetic field gradients may introduce unwanted magnetic field variations. The placement of foreign objects or even the presence of tissue may affect the static magnetic field also. Magnetic measurements may be used for correcting for unwanted magnetic field variations.
A magnetic field probe is a probe or sensor which enables the measurement of spatio-temporal variations in a magnetic field. A magnetic field probe may be constructed by taking a material which has a known Nuclear Magnetic Resonance (NMR) signal. The frequency of specific NMR resonances is a function of the magnetic field. In NMR spectrometers, the magnetic field strength is known and in this way a spectrum may be used to identify the sample. For a magnetic field probe the reverse is true. A known material is placed into a magnetic field of an unknown strength, the spectra or the location of a particular resonance or resonances may then be used to determine the magnetic field strength.
European patent application EP 1 582 886 A1 describes a method of magnetic resonance imaging spectroscopy where additional data is acquired from at least one monitoring field probe positioned in the vicinity of and surrounding an object being imaged, during the execution of the magnetic resonance sequence.
United States patent application US 20090195389 A1 discloses the use of perfluorinated hydrocarbons to construct a field probe.